Compact high speed generator having respective oil and air cooling passages

ABSTRACT

A method for generating electrical power may include the steps of rotating a rotor of a generator at a speed in excess of about 12,000 revolutions per minute (rpm) to about 25,000 rpm and producing power with the generator at a rate in excess of about 800 kilowatts (kW). The generator has a power/weight ratio no smaller than about 3 kW/lbs. A rotor is cooled with cooling oil internally circulated through the rotor of the generator so that contact of cooling oil with external surfaces of the rotor may be precluded. The stator is also cooled with oil that is prevented from contacting the external surfaces of the rotor. Pressurized airflow may be produced in a gap between the rotor and a stator of the generator to preclude entry of cooling oil into the gap.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims the benefit ofU.S. application Ser. No. 14/995,785 filed Jan. 14, 2016 which isincorporated herein by reference in its entirety.

GOVERNMENT RIGHTS

This invention was made with Government support under TacticallyExploited Reconnaissance Node (TERN)—Phase II contract HR0011-13-C-0099subcontract 25172 awarded by DARPA. The Government has certain rights inthis invention.

BACKGROUND OF THE INVENTION

The present invention relates generally to producing high power outputfrom compact electrical generators. More particularly, the inventionrelates to cooling such generators and mitigation of windage losses thatmay result from such cooling.

There is an increasing need for high power generators in the 500kilowatts (kW) to 1 megawatt (MW) range for hybrid-electric propulsionand directed energy weapons. At the same time, these applicationsrequire low weight and volume. Small and light-weight generators must beoperated at high rotational speeds in order to produce high poweroutputs. High amounts of heat are produced during operation of suchgenerators. Oil cooling is typically employed to maintain operatingtemperatures of such generators at a tolerable level.

Oil-based cooling systems are advantageously compact and efficient, butthere has heretofore been a practical limit to their effectiveapplication. At rotational speeds of about 12,000 revolutions per minute(rpm) or more, a generator may experience high windage friction forcesthat develop when oil enters a gap between a rotor and a stator of thegenerator. As the rotor rotates at a high speed, windage friction mayheat the oil in the gap beyond its temperature limit if not replenishedwith an adequate amount of lower temperature oil. This constant oil bathmay have the counterproductive effect of producing higher rotatingfriction or windage reducing the overall efficiency of the generator. Inthat context, heat-reducing benefits of oil-based cooling may be offsetby heat production resulting from windage friction arising from apresence of oil in the air gap. Undesirable windage friction may alsoarise if cooling oil is sprayed in the generator and the oil spray isallowed to contact exterior surfaces of the rotor.

As can be seen, there is a need for generator cooling system that willretain its effectiveness at high rotational speeds. More particularly,there is a need for such a system that may eliminate windage frictionresulting from cooling oil contact with exterior surfaces of a rotorand/or presence of oil in an air gap between a rotor and a stator of thegenerator.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an oil-cooled electricalgenerator comprises: a stator; a rotor; a gap between the stator and therotor; an air passageway passing through the stator to the gap; a sourceof pressurized air in fluid communication with the air passageway; andpassageways for cooling oil, wherein the passageways for cooling oil arefluidly isolated from the gap; wherein the stator comprises a pluralityof laminations; and wherein the air passageway through the statorcomprises a hole in the laminations.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a generator in accordance with anexemplary embodiment of the invention;

FIG. 2 is a cross-sectional view of the generator of FIG. 1 taken alongline 2-2 in accordance with an exemplary embodiment of the inventionwithout an air passageway depicted;

FIG. 3 is a detailed view of a portion of the cross-sectional view ofFIG. 2 in accordance with an exemplary embodiment of the invention;

FIG. 4 is a cross-sectional view of the generator of FIG. 1 taken alongline 2-2 in accordance with an exemplary embodiment of the inventionwith an air passageway depicted;

FIG. 5 is a detailed view of a portion of the cross-sectional view ofFIG. 4 in accordance with an exemplary embodiment of the invention;

FIG. 6 is a partial elevated view of the stator of FIG. 1 in accordancewith an exemplary embodiment of the invention;

FIG. 7 is a flow chart of a method for generating electrical power inaccordance with an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

Various inventive features are described below that can each be usedindependently of one another or in combination with other features.

The present invention generally may provide a system for producing highpower output from a compact electrical generator. More particularly, theinvention may provide a capability for reducing windage friction in thegenerator by precluding entry of cooling oil into an air gap between arotor and a stator, and contact of cooling oil with other exteriorsurfaces of a rotor of the generator.

Referring now to FIG. 1, a cross sectional view illustrates anoil-cooled generator 100 constructed in accordance with an exemplaryembodiment of the invention. The generator 100 may include a housing102, a stator 104 and a rotor 106. A back iron 108 may surround thestator 104. The back iron 108 may be provided with a spiral grove 110along its length. Cooling oil 112 may be circulated through the spiralgroove 110. Thus, the spiral grove 110 may be considered to be acooling-oil passageway 110.

The stator 104 may include windings 114 and laminations 116. Spraynozzles 122 may deliver cooling-oil spray 124 onto the end turns 120.Cylindrical spray shield 126 with internal chambers 127 may bepositioned to deflect the cooling-oil spray 124. First portions 128 ofouter surfaces 130 of the spray shields 126 may be adhesively bonded tothe stator 104. Second portions 132 of the outer surfaces 130 of thespray shields 126 may be sealed against the housing 102 with seals suchas O-rings 134. In other words, the oil spray 124 may be constrainedwithin spray chambers 129 externally of the spray shields 126. Thus,cooling oil spray 124 may be precluded from contacting outer surfaces ofthe rotor 106. Consequently, the rotor 106 may be rotated at a highrotational speed without encountering windage friction forces arisingfrom presence of the cooling oil spray 124 in the generator 100.

Cooling oil 112 may be circulated through cooling oil passageways 137internally through the rotor 106 and through bearings 138 which supporta shaft 140 of the rotor 106. The bearings 138 may be fluidly isolatedfrom interiors of the spray shields 126 with seals 142. Consequently,cooling oil 112 circulating through the rotor 106 may be precluded fromcontacting external surfaces of the rotor 106 even though the rotor 106is advantageously cooled by the cooling oil 112.

Pressurized airflow 144 may be introduced into a gap 146 between therotor 106 and the stator 104. The airflow 144 may preclude entry ofcooling oil 112 into the gap, thus further assuring that externalsurfaces of the rotor 106 are not contacted by the cooling oil 112.

As a consequence of precluding contact of cooling oil 112 with externalsurfaces of the rotor 106, the rotor 106 may be rotated at highrotational speeds without experiencing windage friction forces from thecooling oil 112.

Referring now to FIGS. 1-5, it may be seen how the airflow 144 may beproduced within the gap 146. A source 148 of pressurized air may be influid communication with a port 150 in the housing 102. The port 150 maybe aligned with air passageway 152 that may pass through a land 154 ofthe back iron 108. The air passageway 152 may be in fluid communicationwith an annular groove 156 in the laminations 116 of the stator. Thelaminations 116 may be provided with air-passageway holes 160 passingfrom the annular groove 156 to the gap 146. Consequently, the gap 146may be in fluid communication with the source 148 of pressurized air.

The source 148 may provide pressurized air to the gap 146 so that theairflow 144 in the gap 146 may take place at a pressure of about 3 psito about 5 psi, as an example. The airflow 144 may pass through the gap146 and wedges 164 (described below) can extend all the way down thelength of the core and into the internal chambers 127 of the sprayshields 126. The airflow 144 may emerge from the spray shields 126through drain holes 136. The holes 136 may be positioned so that theyare oriented within the generator 100 to facilitate gravity drain atdifferent generator attitude orientations. With such positioning of theholes 136, the oil spray 124 from the spray nozzles 122 may be precludedfrom entering the spray shields 126 through the holes 136.

FIGS. 4 and 5, shown without the rotor 106, depict an air passageway 152(which can be more than one) in communication, via the annular groove156, with a plurality of air passageway holes 160 (which can be onlyone). From the air passageway holes 160, the airflow 144 can enter thegap 146 adjacent the rotor 106.

By referring now to FIG. 6 which shows a portion of the stator 104, itmay be noted that the stator windings 114 may be held in position withwedges segments 164 that are interlocked with notches formed in thestator laminations 116 that extend along the entire length of the core.The air passageway is 160.

It may be seen that rotation of the rotor 106 may be unencumbered bywindage friction from the cooling oil 122. Consequently, the generator100 may be particularly useful in applications that may require acompact and lightweight configuration for a generator while, at the sametime, producing a high power output. For example, the generator 100 maybe constructed with an overall weight of about 250 pounds to about 300pounds and it may have a capability of generating about 800 kW to about1,000 kW. In order to produce such high power output, the generator 100may need to operate with rotor rotational speeds of about 12,000 toabout 25,000 rpm.

Referring now to FIG. 7, a flow chart illustrates an exemplaryembodiment of a method 700 for generating electrical power with acompact generator that weighs no more than about 300 pounds and canoutput about 1,000 kW of useful electrical power. In other words, thegenerator may have a power/weight ratio of about 3 kW/lbs. Cooling ofthe generator may require extraction of no more than about 21 kW of heatloss energy from the generator when the generator is producing fullpower.

In a step 702, a rotor of the compact generator may be rotated at a highrotational speed (e.g., the rotor 106 of the generator 100 may berotated at a speed of at least about 12,000 rpm). In a step 704, statorwindings of the generator may be sprayed with cooling oil (e.g., Coolingoil spray 124 may be sprayed from nozzles 122 onto end turns 120 ofstator windings 114 of the generator 100). In a step 706, cooling oilmay be internally circulated through the stator spiral groove 110. In astep 708, a rotor of the generator may be cooled with internallycirculating cooling oil (e.g., cooling oil 112 may be circulatedinternally through the rotor 106). In a step 710, airflow may beproduced through a gap between the rotor and the stator of the compactgenerator to preclude entry of cooling oil into the gap (e.g.,pressurized air may be provided from the source 148 through a hole inthe laminations 116 of the stator 104 into the gap 146 to produce theairflow 144, which airflow continues through the spray shields 126 andexits from the holes 136 in the spray shields 126). In a step 712,sprayed cooling oil may be deflected away from the rotor (e.g., thespray shields 126 to deflect the cooling oil spray 124 from the rotor106 so that the rotor 106 is not encumbered with windage friction forcesthat may have been produced by contact with the cooling oil spray 124).In a step 714, electrical power may be produced by the compact generatorat a rate of at least about 800 kW while heat loss energy of less thanabout 21 kW may be extracted by the circulated cooling oil.

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

We claim:
 1. An oil-cooled electrical generator, comprising: a stator; arotor; a housing that houses the stator and the rotor; a gap between thestator and the rotor; an air passageway passing through the stator tothe gap; a source of pressurized air in fluid communication with the airpassageway; oil passageways, around the stator and through the rotor,for cooling oil, wherein the oil passageways are fluidly isolated fromthe gap; wherein the stator comprises a plurality of laminations; andwherein the air passageway through the stator comprise a plurality ofrespective air passageway holes in the laminations; wherein the airpassageway consists of a single, straight path from within the housingand through the laminations; wherein the single, straight path is alongonly one radial line that extends from the gap to the exterior of thehousing.
 2. The generator of claim 1 further comprising: a cooling oilspray nozzle interconnected with a spray chamber surrounding end turnsof stator-windings; a spray shield interposed between the spray chamberand the gap to block oil spray from entering the gap.
 3. The generatorof claim 2 wherein the gap is in fluid communication with an interior ofthe spray shield.
 4. The generator of claim 2 wherein the spray shieldis provided with one or more drain ports.
 5. The generator of claim 4wherein the drain port is located in a position that facilitates gravitydrain at different generator attitude orientations.
 6. The generator ofclaim 1 further comprising: stator windings; and stator-winding supportwedge segments.
 7. The generator of claim 1 wherein the laminations areprovided with annular grooves interconnecting the plurality of theair-passageway holes.